Place steaks in a non-reactive dish. Combine 50ml olive oil, garlic and thyme in a jug, season to taste and pour over steaks, turning to coat evenly, cover and set aside at room temperature.

02

Meanwhile, heat remaining olive oil in a frying pan, add onion slices in a single layer and cook, turning once, until golden (3-4 minutes each side). Pour over vinegar, wine and stock, season to taste and simmer until liquid is reduced to a glaze and onion is tender (4-5 minutes). Set aside and keep warm.

03

Heat a large frying pan over high heat, add steaks and cook until brown and medium-rare (1 minute each side), remove from heat, season to taste and keep warm.

04

Toast sourdough until light golden, spread four slices with aïoli, top with steak, tomato, rocket and red wine vinegar onions. Sandwich with remaining slices and serve immediately with tomato relish, if desired.